The present invention is directed to coating powders for producing coatings that must withstand very high temperatures, such as on barbecue grills or automotive exhaust systems. A coating for a barbecue grill for instance, may be required to withstand temperatures up to 800.degree. F. (427.degree. C.). To obtain a coating which will withstand such high temperatures, it is known to include silicone in the resin. An example of a silicone-containing coating powder, in this case acrylic-based, is found in U.S. Pat. No. 5,422,396, the teachings of which are incorporated herein by reference.
In addition to silicone resin, it is known to incorporate mica as a filler in coating powders, including both acrylic-based coating powders and polyester-based coating powders, to enhance heat-resistance of the coating that is produced.
Polyester-based coating powders containing both silicone resin and mica have been produced that exhibit excellent heat resistance. However, the coatings thereby produced tend to be rough to the touch and tend to mar easily. This phenomena is attributed to high oil absorption of mica.
In order to obtain smoother finishes, it has been attempted to replace or partially replace mica with other fillers, such as wollastonite (CaSiO.sub.3). While a smoother coating initially results, the coating has less heat-resistance, tending to crack at high temperatures. It is a general object of the invention, therefore, to produce coating that is both smooth and highly heat-resistant.